1. Field of the Invention
The present invention relates to an image processing apparatus, a control method of the image processing apparatus, and a program.
2. Description of the Related Art
The reading method for a scanner is divided into a “document fixed reading” method and a “document feeding-reading” method.
The “document fixed reading” method is a reading method in which a document is fixed to the document positioning plate and read by moving a reading unit. The “document feeding-reading” method is a reading method in which a document is fed by an automatic document conveyance and read while the reading unit is fixed.
In the “document feeding-reading” method, if dust (dust, dirt, or stains) is attached to glass in a position where the reading unit is fixed on the document positioning plate, the reading unit continues to read the same dust, which produces a black line in the read image.
FIG. 16 illustrates an image in which a black line appears due to dust when a document is read by a scanner. As illustrated in FIG. 16, the black line appears in a specific position in a main scanning direction with a certain width, which results in a stripe extending in a sub-scanning direction. The image in a black line portion cannot be read accurately in the main scanning direction of the scanner.
A technique for making a black line inconspicuous by detecting dust present in a reading position of a document and performing correction processing on the read image is known as a technique for reducing an appearance of such a black line (Japanese Patent Application Laid-Open No. 2002-185725). According to this technique, dust is detected by reading a white board of an automatic feeding belt of a document and comparing with a threshold a value obtained as a total in the sub-scanning direction of positions in the main scanning direction of black pixels contained in the white board.
In the above technique, a dedicated line memory is needed to store positions in the main scanning direction of black pixels contained in the white board when a dust detection operation is performed.
Thus, to make the dedicated line memory unnecessary, using a region in which no image data is stored of a storage area of a general-purpose image memory allows the region to store positions in the main scanning direction of black pixels contained in the white board can be considered.
However, depending on usage conditions thereof, the image memory may have storage capacity of a region in which no image data is stored of the storage area of the image memory smaller than the capacity of the dedicated line memory. In such a case, a dust detection operation cannot be properly performed by using a region in which no image data is stored of the storage area of the image memory.